Vehicle control systems may be configured to start an engine assuming a given intake manifold volume. However, interactions between vacuum levels in a brake booster and the intake manifold pressure at engine starts can cause variability in the air charge, and consequently air-to-fuel ratio at the engine starts. As such, this increases exhaust emissions.
One approach to address this variability is shown by Kayama et al. in U.S. Pat. No. 6,857,415. Therein, a valve is placed between the brake booster and the intake manifold to equalize the (remaining) pressure in the brake booster to atmospheric levels or to remove air from the intake manifold to the brake booster.
However, the inventors herein have identified a potential issue with such an approach. As one example, the valve used in the approach of Kayama et al. does not allow the level of intake manifold pressure (MAP) to be set from one engine start to another engine start. As another example, even with the valve, a consistent MAP level may not be attained at engine starts occurring at high altitudes as well as at sea level. Further, the valve may be controlled by a control system with electric signals which may increase an overall cost of production.
In one example, the issues described above may be addressed by an aspirator system comprising a volute-shaped aspirator with a linear aspirator protruding through a spiral of the volute aspirator, the volute aspirator comprising a first venturi passage and the linear aspirator comprising a second venturi passage and where the passages are fluidly coupled to a brake booster, and where the aspirators are fluidly coupled to front or rear grills with no other intervening components located therebetween. In this way, vacuum may be provided to the brake booster without flowing suck flow from the brake booster to an engine or any components of the engine.
As one example, the aspirators receive motive flow through the front grill and generate vacuum based on geometries of the linear aspirator, the volute aspirator, and a conical aspirator. The vacuum may be provided to the brake booster when the check valve is open based on a vacuum of the brake booster being less than a minimum threshold vacuum. The vacuum draws suck flow from the brake booster to the aspirator system. The suck flows mixes with the motive flow and flows through the aspirators and out the rear grill without flowing through any other components.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.